The present invention relates to an image forming apparatus of the type developing an electrostatic latent image provided on an image carrier by toner which is supplied from a developing device, transferring the resulting toner image to a transferring material, and removing toner remaining on the image carrier after the transfer of toner image by a cleaning device.
An image forming apparatus of the type described is well known in the art in relation to a printer, a facsimile apparatus, and other equipment. It has been proposed to construct the image carrier, developing device and cleaning device into a unit which is detachable from the housing of the image forming apparatus. With such a unit, one can replace the image carrier, developing device and cleaning device with new ones when the life of any of them expires or replace the developing device which another which contains toner of a different color so as to change the color of development. Usually, the life of a developing device is understood to expire when, for example, the casing of the device storing toner therein becomes empty or almost empty, and that of a cleaning device is understood to expire when, for example, the casing of the device in which toner is collected becomes full or almost full.
In parallel with the recent progress of technology, the life of an image carrier which may be implemented with a photoconductive element by way of example is becoming longer than those of a developing device and cleaning device. In this situation, constructing the image carrier, developing device and cleaning device into a unit which may be discarded when the life of any one of them expires as previously stated brings about some problems from the cost standpoint. Specifically, when the life of the developing device or that of the cleaning device expires, the whole unit including the image carrier which is still usable has to be discarded. Conversely, when the image carrier is scratched or otherwise damaged by unexpected objects or while a trouble caused by a transferring material being transported is dealt with, it has to be disposed of together with the developing device and cleaning device which are still usable. In the case that a plurality of developing devices each containing toner of a different color are prepared to be selectively used, the same number of image carriers as the developing devices have to be used resulting in a prohibitive total cost. Furthermore, when the image carrier is implemented with a photoconductive element, it is necessary for all the openings of the unit to be shielded from light so that the image carrier may be prevented from being affected by light when the unit is removed from the housing of the apparatus. This adds to the production cost of such a unit.
Although image forming apparatuses designed to solve the above problems have been proposed as disclosed in, for example, Japanese Laid-Open Patent Publication (Kokai) No. 61-110168 (Canon), they are not fully satisfactory.